1. Field of the Invention
The present invention relates to an image processing apparatus provided with a frame memory for display, and is suitable in particularly for a case where a high "visualization" performance is required in a video game machine or a graphic computer for forming an image in accordance with pictorial image data which have been compressed and transferred or pictorial image data of the computer graphics.
2. Description of the Related Art
In general, in computer graphics such as, for example, so-called 3D (three-dimensional) graphics, when an "object" having reality (which "object" means an object to be imaged) is imaged, first of all, a surface of the object is decomposed into a plurality of polygons (each of which means a minimum unit of a figure (e.g., a triangular shape or a rectangular shape) to be handled by an imaging apparatus); each polygon is sequentially imaged on a frame memory corresponding to a monitor display image field; the pictorial image data are stored in the frame memory; and the pictorial image data are read out and displayed on the monitor to thereby reconstruct an image which can be stereographically seen.
In some cases, a digital motion picture playback system in which, for example, a secondary memory device such as a CD-ROM having image data recorded in data compression and an image decompression device are used in combination is installed in parallel with such a 3D graphic system. The digital motion picture playback system is inferior in transformation property to the 3D graphic system but has an advantage that an image which is difficult to express in the 3D graphic system may be reproduced. Accordingly, the digital motion picture playback system is used as a subsystem for assisting the 3D graphic system as being used as a background image field.
By the way, in a conventional image processing apparatus provided with such a frame memory (buffer memory) for display, the number of bits of pixels of the image data to be written in the frame memory is in general kept constant. For example, in a game machine or the like, since the pictorial image through the 3D graphics does not require so high image quality, the bit number per one pixel composed of three principal color data R (red), G (green) and B (blue) is kept constant at 15 bits/pixel with 5 bits for each of R, G and B and the resolving power is fixed to 32,000 colors.
The following patent applications each of which is related to the present invention and is owned by the same assignee of the present invention are enumerated and hereby incorporated by reference.
Japanese Patent Application No. Hei 05-190764 (filed on Jul. 2, 1993);
Japanese Patent Application No. Hei 05-258625 (filed on Oct. 15, 1993); and
Japanese Patent Application No. Hei 06-027405 (filed on Jan. 31, 1994).
The U.S. applications corresponding to these Japanese applications are now pending for examination.
As described above, conventionally, the number of bits for one pixel of the frame memory is fixed. Accordingly, as described above, when the motion picture is reproduced and displayed in a system which is the combination of the 3D graphic system and the digital motion picture playback system, even if there is an extra room in a capacity of the frame memory, the bit number is made to be the 15 bits/pixel, as a result of which only the revolving power of 32,000 colors is obtained.
In consideration of the display of the motion picture, it would be possible to fix the bit number per one pixel of the frame memory with, for example, 8 bits for R, G and B and with 24 bits/pixel in order to display 16,700,000 colors. In this case, however, the memory region of the frame memory for the display is unduly increased, and this bit number is not necessary for the pictorial image of the 3D graphics. This approach would not be effective.
An object of the invention is to provide an image processing apparatus which can optimize a bit number per one pixel of a frame memory in conformity with an image quality of an image to be displayed.